Progress in microelectronics, material science, biology and related fields depends on an ever increasing spatial resolution and throughput for the inspection and structuring of the respective specimens. At present, a high spatial resolution can best be achieved with charged particle beam devices such as electron microscopes, focused ion beam devices or electron beam pattern generators that are capable of focusing probing charged particle beams to a sufficiently small focus spot size. Focusing a charged particle beam to a small spot size, however, requires tight control of the focusing electric and/or magnetic fields.
In recent years, it has been recognized that inspections or structuring of micrometer size structures, or below, greatly profit from an operation where the probing or structuring charged particle beam impinges onto a specimen at a tilted landing angle, i.e. at an angle smaller than 90 degrees. Operation at a tilted landing angle can be achieved, for example, by tilting the specimen, tilting the beam optical column, or deflecting the charged particle beam with respect to the specimen.
Unfortunately, as it turns out, focusing the charged particle beam at a tilted landing angle can lead to a deformation or deflection of the charged particle beam in cases where electrical fields are present between focusing lens (objective lens) and the specimen. This in turn may cause image shifts and/or reduced spatial resolution.